This invention pertains generally to printers and display devices in which images are formed by scanning a display medium in raster fashion, and more particularly to a high resolution character generator for generating alpha-numeric and other characters for display in such systems.
Raster scan devices such as cathode ray tubes have been utilized for a number of years to display alpha-numeric characters and other images in a variety of applications including computer output displays. In such systems, a character generator produces electrical signals which modulate the intensity of an electron beam which scans a display screen to form the desired images.
In recent years, there have been attempts to combine character generators with xerographic engines to provide high speed printers for generating original text or other images. In such devices, a latent charge image is formed on the surface of the copy drum or other electrophotographic imaging member of the xerographic engine by scanning the surface with a laser beam or other suitable light beam modulated in intensity by the output signals of the character generator. The charge image is developed and transferred to form a hard copy by techniques similar to those employed in conventional xerographic copy machines.
Character generator driven xerographic printers heretofore provided have been subject to certain limitations and disadvantages. The number of different characters and fonts which can be printed is limited by the memory space required to store them, and some printers can print only a small number of test lines in a fixed format. When the text lines and scan lines extend in different directions on the page, the problem of aligning characters in different text lines limits some printers to characters of a single size or font pitch.